The aim of this proposal is to install an in-vivo neutron activation (IVNA) unit to measure total body carbon (fat) and nitrogen (protein) at the Body Composition Unit at the St. Luke's site in New York City, a major center for body composition research in the country, located in a clinical environment. IVNA has been developed to the status of a criterion method for the measurement of the elements carbon, nitrogen, sodium, chlorine, phosphorus, and calcium, serially, non-invasively, and with safety, in intact human subjects. IVNA has been brought to this level in part through the efforts of our co-investigators at Brookhaven National Laboratory (BNL), through the Program Project Grant NIH DK 42618, of which the PI for this proposal is also the PI. We have completed 815 IVNA studies in 539 subjects under the support of this grant. We now propose to bring a subset of IVNA methods to the St. Luke's site to serve nine NIH-supported projects which extend to completion dates from 1999 to 2003. Three of our proposals are external projects. We shall study 2110 subjects, some of them serially. These human-subject studies are in addition to 624 studies which will be done at BNL on existing protocols. The necessary cross-validations between the BNL and the St. Luke's instruments will be performed with phantoms, and with cross-studies of some subjects who will be studied at both sites. The outcome of this installation will be a large number of studies, in a wide range of subject size, age, race, gender, and clinical status, including subjects with chronic diseases of different degrees of severity. We shall extend our study to the severity of illness in areas where measurement of total body protein metabolism is desperately needed. With IVNA we also will shorten markedly the study-interval and the frequency of studies in patients changing rapidly. The future of body composition research is moving towards the acute care environment; we shall contribute to this necessary transition. Finally, our enlarging "library of normal values" for IVNA (and other) measurements will be available to many investigators and clinicians. We also consider that our IVNA laboratory may be reproduced at many national and international sites utilizing the designs and experience contained in this proposal.